Broad band spherical antenna



y 1962 H. B. RIBLET 3,034,121

- BROAD BAND SPHERICAL ANTENNA Filed Dec. 25, 1959 Y s Sheets-Sheet 1 HENRY B. RIBLET ATTORNEYS May 8, 1962 H. B. INQIBLET BROAD BAND SPHERICAL ANTENNA Filed Dec. 25, 1959 3 Sheets-Sheet 2 HENRY a. RIBLET INVENTOR. v

ATTORNEYS 3 Sheets-Sheet 3 HENRY B. RIBLET INVENTOR.

ATTORNEYS May 8,1962 H. B. RIBLET BROAD BAND SPHERICAL ANTENNA Filed Dec. 23, 1959 United States Patent F Filed Dec. 23, 1959, S91. No. $451,722 8 Claims. or. 343-770 The present invention relates generally to antennas; more particularly it relates to an improved double hemispherical concentric spiral antenna which is especially adapted 'for use with spherical aerial vehicles.

The principal object of the invention is to provide an antennahaving broad band characteristics and a pattern approaching the isotropic (zero null).

Another object of the invention is to provide an antenna which may be flush mounted on the vehicle, so that the aerodynamic stability of said vehicle will be maintained. A further object of the invention resides in the provision of an antenna that may be conveniently arranged on the surface of a sphere, said antenna consisting of pairs of concentric logarithmic spirals placed back to back on the sphere and having such radiation characteristics that received signal amplitude changes would not be greater than 10 db due to antenna pattern variations, regardless of the attitude in space of the sphere.

Other objects and many of the attendant advantages of this invention, will be readily, appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram showing a logarithmic spiral;

FIG. 2 is a diagram showing the evolution of a logarithmic spiral slot;

FIG. 3 is a diagram showing a double spiral slot, the two slots being positioned 180 degrees with respect to each other;

FIG. 4 is a perspective view of the improved spherical antenna;

FIG. 5 is a plan view showing a pair of concentric spiral antenna elements as they would appear if arranged in a plane;

FIG. 6 is a perspective view of a hemisphere with one pair of the concentric spiral antenna elements thereon;

FIG. 7 is a diagram showing a basic pattern obtained with a spiral antenna arranged on the surface of a hemisphere; and

FIG. 8 is a diagram showing the pattern obtained by placing two pairs of hemispheric spiral antennas back to back on a sphere, it being assumed that feed point phasing and orientation of the spiral pairs with respect to each other are correct.

The requirement for a broadband antenna, covering a frequency range of at least four to one and providing radiation characteristics which would produce no nulls greater than l0 db with respect to the maximum in any plane, and at any angle with respect to the antenna within a spherical boundary, was generated by the development of a special spherical aerial vehicle. This requirement was so imposed that regardless of the attitude of the vehicle in space, the received signal variation would not be greater than 10 db due to antenna pattern changes.

The design of the antenna constituting the present invention is based on the established properties of the class of broad band antennas using equiangular spiral slots or conductors. Such an antenna has the property that its shape is specified entirely by angles, so that its performance is independent of wavelength. A familiar example of such an antenna is the infinite biconical horn.

The logarithmic spiral has the property that an angle between the tangent to the curve and its radius vector is 1 on the surface of a sphere.

3,034,121 Patented May 8,1962

a constant and greater than 90 degrees. Such a spiral is shown in FIG. 1. A spiral slot antenna can be constructed by plotting two spirals slipped in angle with respect to. each other, as shown, in FIG. 2. Similarly, as shown in FIG. 3, a double spiral slot can be produced by plotting two spirals (FIG. 2) 180 degrees with respect to each other. In FIG. 3 the feed points are shown at X-X.

The present invention contemplates the application of a logarithmic spiral antenna to the surface of a hemisphere rather than to a flat surface or sheet as in conventional practice. More specifically, and as shown in FIG. 4 of the drawings, the present invention utilizes a pair of concentric logarithmic spiral antennas applied back to back The sphere is shown at 10 and is mounted on a suitable support 12 which also carries the feed line, to be described hereinafter. passes through the equator of the sphere, indicated at 14, and is "thus positioned normal to the polar axis of the sphere. Suitably secured to or formed on each half of the sphere is a pair of concentric spiral logarithmic an- 'tenna'elements .16 and 18 separated by dielectric filled in FIG. 3.

.the surfaces 19 are opened at the poles of the sphere and the feed means connected to them across the slot as shown Since either embodiment is the complement of the other the radiation characteristics will be essentially the same for each case.

As shown in FIG. 6, a central coaxial feed line 20, which is passed upwardly through the support 12, transfers energy between a transmitter or a receiver and the antenna elements 16 and 18, branch feed lines 21 and 22 connecting the central line to said elements. The branch feed lines 21 and 22 are, as shown in dotted lines, arranged in spiral formation within the hemisphere and beneath, or inside, the antenna elements.

When the spiral antenna is formed on the surface of a. hemisphere, a radiation component is available normal to the polar axis of the hemisphere, giving some side radiation. Such radiation is similar to the null fill-in obtained by a bent dipole or a V-shaped dipole. FIG. 7 is illustrative of this result. The dotted back lobe illustrates the back radiation if the cavity within the hemiphere is not infinite or not fully shielded.

If two hemispheres are placed back to back to form a sphere and the orientation of the spiral and the feed point phasing are correct, the radiation components at the equator can be made to be in phase. In this situation the radiation components normal to the polar axis (i.e., equator) add to reinforce the side nulls already filled in by the bending of the spiral slot or conductor antenna elements over the spherical surface. FIG. 8 shows the arrangement.

When the two spirals which are fed independently at the poles are fed in phase, by equal length lines, from a common point and the radiation components are in phase all around the equator, the radiation pattern is a figure of revolution about the polar axis. By another phasing arrangement (i.e., out of phase 180 degrees) a null of revolution will be obtained about the equator and a pattern equivalent to that produced by the open flat plane spiral slot and spiral conductor will be obtained. By winding the spirals in the same screw sense rather than opposite, the phasing will vary from in phase in one plane to out of phase in a plane normal thereto, creating zero nulls in one plane and fill-in of the nulls in the plane degrees removed.

The support 12 7 Obviously many modifications and variations of the .present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. -What is claimed is: a

1. In an antenna, a pair of hemispherical body members of dielectric material forming asphere, a support for the-sphere,}said supportextending normal to the axis of said's'phere,electromagnetic field producing means on the respect to a diameter of said sphere as concentric logarithmic spirals at the surface of the sphere, one pair of the elements being located on one of the hemispherical :body members with the inner ends of said'elements adjacent the polar aids of the sphere iand the other pair of said elementsbeingpositionedonthe other of the body members in back to' backrelation to the firstpair of elements.

2. An antenna as recited in'claim :1, in'cludingadditionally means for transferring electrical energy between the center of the sphere and a point remote from the sphere; and-means connecting saiddast-mentioned means 'to theinnerends of the elements ofeach pairof elements. 3'. Imam-antenna, a spheretof dielectric material, a pair ofc'onduc tors arranged with respect to a diameter of said sphere in concentric-logarithmic spirals onfeach'half of the sphere; the pair'of conductors on one half of the sphere being positioned backto back with respect to the pair-of conductors on the other half of the sphere, and means for transferring electrical energy between feed points onthepairs of spiral conductorsand a point remote Ffrom-the-antenna.

4. :In an antenna, "a sphere, electromagnetic field producingmeans,-said means comprising pairs of substantially concentric equia ngular spiral elements arranged on the "surface of the sphere so that the'inne'r ends of said elenients are positioned on the axis of the sphere and the router endsjof said elements are positioned in juxtaposed sphere and comprising pairs of elements arranged with said spheres are in phase.

7 7. An antenna as defined in claim 3 wherein said hemispheresflare oriented .with respect to one another so that the radiation components at' the equator of said sphere are in phase. 7

8. An omnidirectional antenna comprising a sphere, and electromagnetic ifield producingmeans, said means comprising pairs of substantially concentric equiangular spiral elements-arranged oneach of the hemispheres defining said sphere .so Ithat the radiation components from 'saidelements are in phase aroilnd the entire equator of said sphere. i

:References Cited in the {tile of this patent aUNITTED ST TES PA ENI 1,688,229 Enge bretsen Oct. 16, 1928 1,755,012 Matheson' Apr. 15, 1930 2,179,257 'Goloviznin' Nov. 7, 1939 2,863,145 Turner Dec. 2, 1958 Q HERRE ERENQE V Du Hamel and Isbell article, IRE Convention Record, Part I, 101. 5, March 18, 1-957, pages 1194-25. 'Aviation =Week, July 14, .1958, pages 82 yol. 69.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION a tent Noe 3.034 V 121 May 8 1962 Henry B, Riblet the above numbered petthat error appears in nt should read as It is hereby certified that the said Letters Pete ed this 13th day of November 1962.

d sphere are in fOI "equitrian 1.1531

ed Oil each Of phase 1 elements arrang the he e Signed and seal SEAL) ERNEST w. SWIDER DAVID LADD Commissioner of Patents \ttesting Officer 

